This invention relates to a coaxial microwave attenuator for high power, which operates independently of the frequency and in particular one having a fixed or adjustable structure. Such attenuators are frequently used in high frequency and microwave techniques.
In wave guide systems there is a clear tendency to increase the powers transmitted. Coaxial components such as attenuators or terminal resistors adapted to frequencies of more than 4 gigahertz and to powers greater than 10 watts are difficult to find on the market.
Fixed attenuators of a conventional type for frequencies ranging up to 18 gigahertz will only carry loads of a few watts. Such units are often grouped in the form of large cylindrical adjustable attenuators. If it is desired to obtain a graduation corresponding to variations of 1 decibel such attenuators are expensive. The coaxial or flat resistors of conventional attenuators are for the most part mounted on the inner conductor. This results in an undesirable transfer of heat to the more massive parts of the external conductor of the attenuator, which explains its low maximum load. If attenuators having directional couplers are used, it is possible to increase the maximum load by placing at the end of the direct line of the coupler a resistance having a high loading capacity. When the line is coupled one may, however, accommodate a minimum attenuation of about 10 decibels, which is often not very desirable.
In French Pat. No. 70.06639, an attenuator is proposed in which most of the aforesaid deficiencies are avoided. In order to obtain over a large band (for example 10:1 and more) an attenuation curve which is independent of the frequencies, one is also obliged, in this solution, to combine various individual absorption members assembled in series, one after the other, into a complete attenuator.